During the past few years there has been a substantial growth in the production of high-strength paper and cloth products having a nonwoven, randomly-oriented structure, bonded with a polymeric resin binder. Such products are finding wide use as high-strength, high-absorbency materials for disposable items such as consumer and industrial wipes or towels, diapers, surgical packs and gowns, industrial work clothing and feminine hygiene products. They are also used for durable products such as carpet and rug backings, apparel interlinings, automotive components and home furnishings, and for civil engineering materials such as road underlays. There are several ways to apply a binder to these materials including spraying, print binding, and foam application. Further, depending on the end use, various ingredients such as catalysts, cross-linkers, surfactants, thickeners, dyes, and flame retardant salts may also be incorporated into the binder.
In the high-speed, high-volume manufacture of cellulosic products such as wet wipes, an important binder property is a fast cure rate; i.e., the finished product must reach substantially full tensile strength in a very short time after binder application so that production rates are not unduly slowed down. In these products, such a property is usually obtained by using a binder which is either self cross-linkable or by incorporating an external cross-linker into the binder formulation. The cross-linker or self cross-linkable binder apparently not only interacts with the binder monomers but with the hydroxyl groups on the cellulose fibers as well to quickly form very strong bonds.
The most commonly used binder formulations include copolymers in which one or more of the comonomers is an ethylenically unsaturated mono- or dicarboxylic acid or a derivative thereof. For example, carboxylated styrene-butadiene resin (SBR) copolymers, carboxylated acrylate copolymers and carboxylated vinyl acetate/acrylate copolymers are used extensively as binders for nonwoven cellulosic materials to impart desired strength characteristics.
As the need for stronger nonwovens developed, cross-linking agents for the base binders were utilized. N-methylolacrylamide and other similar cross-linkers were incorporated into the binders. While the strength of the nonwovens increased desirably, it was discovered that many of these cross-linking agents, especially N-methylolacrylamide and similar materials, emitted formaldehyde during use. The toxicity of formaldehyde caused users to search for non-formaldehyde emitting alternatives. One of the non-formaldehyde emitting cross-linkers is methyl acryloamidoglycolate methyl ether (MAGME). However, while MAGME improved the strength of many copolymeric binders and did not emit formaldehyde, it was observed that the use of MAGME with carboxylated copolymers did not produce the increases in strength expected to the same degree as with non-carboxylated copolymers. A way to use MAGME with carboxylated copolymers without sacrificing binder strength was therefore needed.